Accuracy of three digital waxing-guided trial restoration protocols for controlling the depths of tooth preparation for ceramic veneers

Statement of problem. The accuracy of digital waxing -guided trial restoration protocols that have been implemented with ceramic veneers has not been reported. Purpose. The purpose of this in vitro study was to evaluate the accuracy of 3 digital trial restorations fabricated from digital waxing for ceramic veneers. Material and methods. A uniform 0.3 -mm digital waxing added to the facial surface of 30 maxillary central typodont incisors was created in a software program. The trial restorations were fabricated on typodont teeth with autopolymerizing acrylic resin by using a silicone index based on 3 -dimensionally printed casts designed from the digital waxing. The 30 maxillary central incisors were divided into 3 groups: the depth cutter (0.5 mm, Komet) (DC) group, the round bur (1.5 mm, Diatech) (RB) group, and the specially designed calibrated depth bur (laser mark of 0.5 mm, Gaofeng) (CD) group. The 3 groups were randomly prepared with a random number table by 2 experienced prosthodontists aiming to produce an even facial clearance of 0.5 mm. The dimensional differences in the standard tessellation language (STL) files between the surfaces of the original teeth, digital waxing, trial restorations, and prepared teeth in the software program were measured and analyzed at the same 9 points on the labial surface. One-way ANOVA with a post hoc test was used to identify significant discrepancies between trial restorations and waxing and differences in the reduction depth of typodont teeth (RDT) and the reduction depth (RD) among the 3 techniques (a=.05). The mean relative differences (MRDs) were calculated to determine the accuracy (%). Results. The thickness of the trial restorations was significantly greater than that of the digital waxings, with a discrepancy of 0.20 +/- 0.14 mm, especially at the cervical site. With the use of a trial restoration, the RDTs of the middle (-0.01 +/- 0.11 mm) and cervical locations (0.09 +/- 0.20 mm) showed significantly smaller preparation depths than did the other locations. Significant differences in RD were found among the 3 guided techniques (P<.05). Group DC presented the most accurate result of 0.51 +/- 0.08 mm with an MRD of 2%, whereas the results of 0.57 +/- 0.10 mm with an MRD of 14% and 0.60 +/- 0.11 mm with an MRD of 20% were obtained from group RB and group DC, respectively. Conclusions. The trial restoration was significantly thicker than its corresponding waxing. The DC technique presented the most accurate reduction result among the 3 protocols examined.